When an accident causes Dr. McCoy to go temporarily insane, he escapes to a strange planet. There, the search party discovers a device left by a superior, vanished civilization, a time portal that plays the history of Earth for them - but then Bones jumps through it into the past, causing a change in history important enough to make the Enterprise vanish. Kirk and Spock, who fortunately made a tricorder recording, must attempt to go through to just before McCoy's arrival and stop him from changing history in the United States during the Great Depression, where they have no advanced technology available.
Did You Know?
Edith Keeler tells McCoy his blue uniform hardly looks like it's from the United States Navy. DeForest Kelley
filmed naval training videos in real life. See more
When McCoy changes history, the Enterprise vanishes because it no longer exists in this new time-line. But the landing party would have also vanished. See more
Captain's log, no stardate. For us, time does not exist. McCoy, back somewhere in the past, has effected a change in the course of time. All Earth history has been changed. There is no Starship Enterprise. We have only one chance. We have asked the Guardian to show us Earth's history again: Spock and I will go back into time ourselves and attempt to set right whatever it was that McCoy changed.
Script Supervisor is written as "SCPIPT SUPERVISOR...GEORGE A. RUTTER" in the credits. This happened on at least two other episodes in season one. See more
More recent prints omit the shot in which Rodent accidentally vaporizes himself with McCoy's phaser. Instead, the scene ends with him standing in the alley near the collapsed McCoy and looking bewildered. See more
Featured in Cosmic Thoughts
Written by Ray Noble
, Jimmy Campbell
and Reginald Connelly
(as Reg Connelly)
Heard playing from the radio repair shop (with an uncredited vocal performer) and later as part of Fred Steiner's instrumental score (also uncredited)
Due to copyright issues, this music was replaced on some releases in the 1980s and 1990s See more